I don't know man. As far as my research goes, the environmental impact of Bitcoin is basically nothing compared to the environmental impact of the cash system. There's already an increasing and improving way for Bitcoin to be mined without causing much to the environment so it won't really matter.
Instead of asking those mining enthusiast to come up a way or a solution to the problem (which I think they are doing already), why don't you do something yourself? Maybe plant a tree or something. Maybe donate to those environmental charities. Because no matter how many rants you make here in the forum but as long there is money, miners will mine they want even if the cost is a slight change in the environment.
Maybe make a movement yourself about helping the environment. I'm sure some of the members here in the forum will be willing to help you.
Indeed most people able, should plant a tree. Not just one, many, make it an activity and do it from time to time. Just make sure to use a local species, don't want to make the problem worse.
You could argue modern lifestyle is making this irreversible. The weather patterns are changing worldwide, and solutions are not coming from the top, the politicians are worthless.
I'm not a fan of donations, for all you know, they might be misused (which is why i warned NOT to give anything for the Amazon). Get involved and plant a tree yourself, how hard can it be? And then do it again, and again, and again. Make it a social activity.
If its close to the place you live, try to take care of it as well.
Truly disappearing Bitcoin won't change things, and as explained before the market itself is solving this issue on its own.
You could also change some habits, reduce, reuse and recycle; cycle to work, invest in renewable: buy a solar panel with a grid tie inverter, etc.
I wonder if modern society is sustainable. Are you willing to change some habits? Americans have a huge problem, they went to live too far away from work, and waste too much commuting. Telecommuting may help. One of the reasons USA is one of the top polluters is their car dependency, while its perfectly fine to live in countries in Europe and Asia, the typical sub-urban American cannot think of living without owning a car, and they even designated a car type for this lifestyle (which happens to be a fuel waster).
Unfortunately China is copying this bad example, what Americans did in the 50ies (the freeways program) has been reproduced in China, complete with the madness car production, as a "means to push the economy". These two countries alone are the most responsible.
Give a satoshi to plant a tree? No, go plant it yourself, you lazy couch potato.